Advantages of stringing power conductor cables by electric utility companies within transmission and distribution networks using helicopters to advance a conductor towing line or sock line already threaded through a stringing block suspended from an insulator or other tower structure on one tower, to the next tower are well known. However, before the helicopter can advance to the next tower, the sock line must first be placed onto the pulley of the stringing block which at least requires an additional step to be taken by the helicopter pilot if the process is to be accomplished from the air, complex hardware must be mounted on the tower being strung, or at least one person must be located on the tower in the helicopter wash during the stringing process.
Stringing blocks having sheaved wheels and spring-biased fly gates and helicopter loading arms are generally used to facilitate side-loading of power conductor cables. This technology has been useful only for transmission cables hung from portions of a tower which can be accessed from above or from the side. That is, towers having an upper cross support, but no side access, for example, electrical conductors surrounded by a closed-sided, window-like structure, have not been threaded by aircraft using such blocks.
Airborne stringing of a sock or threading line through power line towers having no side access, however, has been described using elongated threading members having the sock line secured to the trailing end thereof, having leading and trailing helicopter hoist line coupling parts for facilitating the suspension of the threading members from an aircraft, and having at least one tower catch for holding the threading member on the tower structure while the hoist line is released and reattached to the threading member. The latter operation has been carried out entirely by the aircraft without the necessity of personnel or apparatus on the tower during the proximity of the aircraft thereto, but requires an additional step by the aircraft pilot of moving the sock line onto a pulley.
Accordingly, it is an object of the present invention to provide an apparatus and method for airborne threading a sock line through a block having a pulley disposed on a tower.
It is also an object of the present invention to provide an apparatus and method for airborne threading a sock line through a block having a pulley centrally disposed on a tower and surrounded by a closed-sided, window-like tower structure.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.